The present invention relates generally to local area networks of transceiver units interconnected by a data bus, and more specifically to a transformer bus coupler for connecting a transceiver to a data bus line.
Most data bus couplers which are presently in use are a source of discontinuities between the transceiver units and the data bus. These discontinuities occur because the impedance of each data bus coupler is commonly different from the characteristic impedance of the transmission line.
The task of effectively coupling remote equipment together in a local area network is alleviated, to some extent, by the coupling network disclosed in the following U.S. patents, the disclosures of which are incorporated by reference.
U.S. Pat. No. 2,148,098 issued to Bowman-Manifold;
U.S. Pat. No. 2,237,796 issued to Smith;
U.S. Pat. No. 3,983,323 issued to Griffith et al;
U.S. Pat. No. 4,443,662 issued to Nakhla;
U.S. Pat. No. 4,507,793 issued to Adams; and
U.S. Pat. No. 4,588,856 issued to Cohen.
The Nakhla patent shows a coupling network for coupling data signals to and from a telephone subscriber line. The network serves to couple data from a modem at the central office end of a line to the line for transmission to the subscriber end modem and also serves to couple data from the modem via the line to another modem in a full duplex manner.
Bowman-Manifold shows a high frequency transmission line with a receiver or branch line and series impedances both having a value R.sub.1 /2. By in effect forming a resistant T-network at a load tapping point the patent alleges that substantially no reflection is introduced at the tapping point.
Smith is directed to a mixer circuit in which a plurality of devices are connected to a pair of buses by a fixed attenuator having series and shunt impedances. Griffith et al are concerned with a balanced bridge, full duplex system for sending and receiving digital signals. Cohen and Adams both relate to digital signal transmission and reception of a common line.
While the systems described in the above-cited references are instructive, the need for connecting transceivers to data bus lines without impedance discontinuities remains. The present invention is intended to satisfy that need.